Tank stats

72G, EI for 2 months 60-80 gallon guidelines, 260W CF lighting, pressurized CO2 30ppm (DC 4dKH solution), water is 9-10 GH from the tap so I don't add anything but the ferts and traces. No algae issues.

I stopped dosing the KNO3 because my nitrates would climb above 30 ppm. No matter what they seem to stay at 20 ppm (verified with 2 different tests). Fish load is moderate, I suspect it is because of the Wet/Dry filter that has been running with bioballs for the year. I know SW aquarists frequently take out the bioballs because they supposedly cause nitrates.

My concern is that without dosing the KNO3 the plants could become K limited, would it be a good idea to dose more KH2PO4 then the 3/16 recommended? I think I have read that increasing PO4 sometimes encourages the use of NO3.

Thanks